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What is an Antibody Test?

How Can Previous Coronavirus Infections be Detected? 

Medical laboratories are currently doing blood tests to detect the presence of antibodies, which determine whether there has been a previous Covid-19 infection. In fact, the test consists in detecting the presence of antibodies in a blood sample to determine if the person has previously been infected with the virus, and thus has developed components to fight a future infection. 

The antibody test is a screening for what is known as “antibodies” in the blood, which are developed by the body when fighting any viral infection such as Covid-19. This technique is known as ELISA and is an enzyme immunoassay that shows whether the person has previously been infected with the virus. 

Antibodies are proteins produced by the body to protect itself from any foreign body it is exposed to, i.e. when fighting an infection. The test requires taking a blood sample by a specialized laboratory expert. The sample is then placed on a dish that contains the specific antigen to be detected. If the blood contains antibodies to this antigen, the two will bind together, and then a change in the color will be noted. In turn, the change in color is measured to give an impression of the quantity of antibodies present in the body, and then the result is sent to the specialist doctor to be read and to diagnose the condition.

Whenever a virus enters the body, the immune system works on fighting it by developing antibodies. A blood sample is therefore taken and placed in a thin plate, along with a chemical solution, and it is analyzed. The antibody test indicates the number of people who previously contracted Covid-19 and recovered from it, including asymptomatic people, which helps determine persons who developed an immunity against it. However, it is still unknown how strong and persistent that immunity is. 

To reveal the presence of a previous infection with the novel coronavirus, the doctor determines one or two types of antibodies to search for, i.e. the antibodies to SARS-CoV-2, which is the virus that causes COVID-19. If the antibodies – called IgM and IgG – are indeed present, the color of the sample changes, which means that this person was infected with the virus and had immunity to it.

IgM antibodies appear at an early stage of the infection. IgG antibodies are likely to appear at a later stage and are more like a long-term memory – in the sense that the immune system preserves them, and in the event of exposure to infection in the future, it will be able to fight it. However, doctors and researchers have yet to know how long this takes in the case of novel coronavirus.

The importance of this test lies in determining three possibilities: whether the person is not infected, whether they are currently infected and have a type of antibody developed by their immune system fighting the virus, and the third possibility is that they had been infected with the virus and recovered from it. The third scenario means they have antibodies that can fight infection again without achieving immunity and prevention from a new infection.

These antibodies remember the virus during a possible second exposure. They mobilize the immune system to halt the disease again. However, what needs to be known is that it has not been established how effective these antibodies are at fighting a second infection, how many antibodies the body needs for a successful immune response and for how long the antibodies will stay with you – will they be kept for a few months or for years? The answers to these questions need more time as we try to understand this novel virus.

The benefit of this test lies in the fact that people who have recovered from Covid-19 may be eligible to donate blood plasma to treat other people whose condition is critical, so that their ability to fight the virus is enhanced. The issue here needs more tests to determine the effectiveness of treating patients with the plasma of recovered patients.

Among the benefits of the test is also helping researchers and scientists detect the characteristics of the virus, and to understand if recovered patients are immune to the virus or not. It also helps epidemiologists to know the number of people who were infected in the past and were not counted in official statistics, and it helps to know whether the numbers indicate access to a type of herd immunity in the community. This helps decision-makers in countries to take appropriate measures to ease or tighten the imposed restrictions.

The antibody test also helps in the vaccine tests run on volunteers to follow the reaction of their immune system, and through this test, it is possible to follow up the immune system of people who have already been infected with the coronavirus and have been cured of it. 

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